First, you should look at your tank's combat log to see what is killing your tank. After Gift of the master, Kephess should do a leap (to close in onto the tank), a knock back (up to 18k, depending on tank), and then cast Breath of the Master. Your tank's health should be topped up during the last few ticks of Gift of the Master. If that is not happening, then your healer must be healing themselves instead of the tank.